Bringing a new focus to the training and advising mission while pushing Afghans to take the lead in security operations, up to eight newly designed units -- dubbed security force assistance brigades -- will replace an equal number of Army brigade combat teams across the east and south of Afghanistan by next spring.

Not only will the new brigades focus more on training and mentoring Afghan National Security Forces than leading combat and counterinsurgency missions, but they will also deploy at about half of the strength of the brigade combat teams they're replacing. Each security force assistance brigade is 1,400 to 2,000 soldiers, as opposed to the 3,500 to 4,000 soldiers in a fully manned brigade.

The move has major implications for the mission in Afghanistan, as the number of U.S. forces will probably decline as smaller brigades take the place of their larger predecessors, and Afghan forces take the lead in planning and executing operations. There are 68,000 U.S. service members in country. Roughly 40,000 of those are soldiers.

Pentagon and Army officials stress that no final decision has been made on the size of the U.S. contingent in Afghanistan in the run-up to the White House-imposed December 2014 conclusion of combat operations, but Army Chief of Staff Gen. Ray Odierno said last week that he expects some decisions to be made over the next month.

"The first decision that has to be made is, what are we going to leave behind after 2014?" he said. "I believe that that decision will be made after the first of the year, but we haven't even started intense discussions on it yet."

At their core, the brigades will be made up of a number of security force assistance teams of 10 to 20 officers and noncommissioned officers each, who will rely on the remainder of the brigade for their security, logistics, intelligence and joint fires needs.

While individual teams have deployed throughout 2012 to mentor Afghan forces, they have been forced to rely on whichever brigade owned the battlespace for security, transportation, intelligence and logistics. This added to the brigade's workload and, at times, caused some friction between the teams and the host brigade since the teams' goals didn't always align with those of the brigade commander.

The problem was that the two groups had not worked together prior to deployment. The small size of the teams also put them at risk of green-on-blue attacks since they weren't large enough to provide for their own security.

The new model gives these teams their own security, joint fires, intel and logistics capabilities so they can function independently.

"Although they won't take the whole brigade," Odierno said, "this will allow us to take the soldiers and leaders (needed for training), and who will also provide security for those teams. It integrates them into unity of command and unity of effort. It's something similar to the brigades that we established there at the end in Iraq. So I think this is the right way to go."

The deployments mark a major shift in the way the Afghanistan fight is being waged, said Army Col. Randy Lane, chief of campaign plans at International Security Assistance Force headquarters in Afghanistan. "Arguably, the most important thing we have to do now is not the fighting, but instead enabling the Afghans to secure themselves, and we think that this is the best way forward."

By next December, a year into the security force assistance brigades model and a year away from the end of combat, International Security Assistance Force leadership expects to see the Afghans operating independently, with some advisers continuing to work closely with some brigades. The Afghans "will be out there and really conducting all of the operations from police all the way up to COIN operations, and leading this all the way into the (Afghan) presidential elections in April 2014," Lane said.

The brigade concept also paves the way for an enduring training mission that will last beyond the December 2014 drawdown date originally outlined by President Barack Obama. Over the past year, the 2014 date has been transformed, with little public debate, from what was initially considered the end of U.S. involvement in fighting the Taliban to the beginning of what is merely a smaller footprint for U.S. forces in Afghanistan.

In comments during a swing through Asia on Nov. 12, Defense Secretary Leon Panetta told reporters that outgoing International Security Assistance Force chief Marine Gen. John Allen was working on plans to identify the right number of troops to stay behind for "the post-2014 enduring presence." It would include missions such as counterterrorism, training, advising and assisting the Afghan army and police.